Balantidium Coli PDF

BALANTIDIUM COLI Balantidium coli belongs to the phylum Ciliophora, class Litostomatea, order Vestibuliferida and family Balantidiidae. This was first discovered by Malmsten in 1857 in the faeces of two patients with acute dysentery. Geographical distribution B. coli is worldwide in distributi...

BALANTIDIUM COLI Balantidium coli belongs to the phylum Ciliophora, class Litostomatea, order Vestibuliferida and family Balantidiidae. This was first discovered by Malmsten in 1857 in the faeces of two patients with acute dysentery. Geographical distribution B. coli is worldwide in distribution. Because pigs are an animal reservoir, human infections occur more frequently in areas where pigs are raised. Other potential animal reservoirs include rodents and non- human primates. Habitat B. coli inhabits the large intestine of man, monkeys and pigs, where the trophozoites feed on cell debris of the intestinal wall, starch grains, bacteria, and mucus as lumen parasites. It is generally believed that pigs act as the main reservoir for human infections. Morphology B. coli is the only pathogenic ciliate and is the largest protozoal parasite inhabiting the large intestine of man. It has a trophozoite and a cyst stage (Fig. 6.1). The trophozoite is found in dysentric stool. It is actively motile and is the invasive stage. On the other hand, the cyst is found in chronic cases and carriers. It is the resistant form and the infective stage.  TROPHOZOITE It is an oval organism, measuring 60 x 45 μm or more. The anterior end is somewhat pointed and has a groove (peristome) leading to a mouth (cytostome) terminating in a short funnel-shaped gullet (cytopharynx) extending up to anterior one-third of the body. There is no intestine. The posterior end is broadly rounded and has an excretory opening known as cytopyge (Fig. 6.1) through which the residual contents of food vacuoles empty periodically. The body is covered with a delicate pellicle showing longitudinal striations. Embedded in the pellicle are short cilia of relatively uniform length that, in the living organism, maintain a constant synchronized motion that vigorously propels the protozoan forward. The cilia that line the mouth part are longer and are called adoral cilia. These are used for propelling food into the cytopharynx. The cytoplasm of the trophozoite has: 1. Two nuclei: a macronucleus which is large and situated near the middle of the body. It may be kidney- shaped, spherical, curved or elongate. The micro- nucleus is small, round and lies in close proximity to the macronucleus. 2. Two contractile vacuoles: which may lie side by side or one above the other. These vacuoles are responsible for maintaining the proper osmotic pressure in the cell by drawing excess water from the cytoplasm and ejecting it to the exterior. 3. Numerous food vacuoles: The food particles on being ingested become surrounded by a vacuolar membrane and digestion takes place inside the vacuoles. The parasite is capable of ingesting a variety of food particles, such as bacteria, starch grains, fat droplets, cell debris of the intestinal wall, red blood cells, etc. CYST The cyst of B. coli is spherical or oval measuring 40 - 60 𝜇m in diameter. It is surrounded by a thick and transparent double-layered wall. Newly formed cyst shows movement, but as the cyst matures the cilia are absorbed and the movement ceases. The macronucleus, micronucleus and vacuoles are present in the cyst also. Unlike encystation in amoebae, in n B. coli this s is not preceded by complete discharge of undigested foods. CULTURE B. coli can be cultured in all the media that support the growth of E. histolytica. LIFE CYCLE B. coli passes its life cycle in two stages, but in one host only. Pig is the natural host and man is incidental host. Transmission occurs from pig-to-pig, pig-to-man, man-to-man and man-to-pig. Pig-to-pig transmission is very common. The cyst is the infective form of the parasite. Man acquires infection by ingestion of food and water contamination with the faeces containing the cysts of B. coli (faecal- oral route). Excystation occurs in the small intestine and multiplication occurs in the large intestine. From each cyst, a single trophozoite is formed (Fig. 6.2). The trophozoites feed on bacteria and faecal debris, multiply by transverse binary fission, and form cysts (encystation) that pass in the faeces. B. coli reproduces by transverse binary fission. First the micronucleus divides into two, then the macro- nucleus and finally the cytoplasm separates into tWo a daughter organisms by a transverse partition in the middle of the body. The daughter organism formed from the anterior half retains the cytostome of the original parasite but develops a new excretory pore, whereas the one formed from the posterior end develops a new mouth. Sexual union (syngamy) is an important aspect of this parasite's life cycle. It occurs by a process of conjugation, in which two cells come in contact with each other at their anterior ends and exchange nuclear material. Conjugation lasts for a few moments, after which the cells detach. There is no increase in numbers as a result of conjugation. Encystation of the trophozoite occurs as it is being transported down the intestine. In this process, the organism partially rounds up, then, without completely retracting the cilia, it secretes a tough cyst membrane. In the infected person the parasite may be passed in the faeces as a trophozoite or a cyst. The trophozoite does not encyst outside the body and disintegrates. The passed cyst survives and may contaminate food and water and, as a result, may then be passed to other humans or animals.  PATHOGENICITY Most infections with B. coli are apparently harmless. However, rarely, the trophozoites invade the mucosa and submucosa of the large intestine and terminal ileum and produce ulcers or subsurface abscesses in the mucous or submucous coats that sometimes extend to the muscular layer. The ulcers are round, ovoid, or irregular in shape with undermined edges. The floor of the ulcer is covered with pus and necrotic material. The abscesses are usually small and, when incised, are found to be filled with a mucoid material containing numerous balantidia. The intervening mucosa may or may not be inflamed. On microscopic examination, parasites are frequently seen in clusters in the submucosa or at the bases of the crypts. They can easily be recognized because of the presence of the macronucleus which stains deeply with haematoxylin and eosin. The cellular response is mainly lymphocytic with some plasma cells being present. Neutrophils are few unless there is a superimnposed bacterial infection. Sometimes the parasites may invade the regional lymph nodes and they may be detected inside the lymphatic tissues. B. coli can produce hyaluronidase, which probably helps it in its invasion of the host tissues by dissolution Alar ground substance. Chronic recurrent diarrhoea, alternating with constipation, is the most common clinical manifestation, but there may be bloody mucoid stools, tenesmus, anorexia, nausea, epigastric pain, vomiting and intestinal colic. In a majority of patients, recovery occurs in 3 - 4 days even without treatment but extreme cases may mimic severe intestinal amoebiasis. In patients with acute infection, extraintestinal involvement such as liver abscess formation, peritonitis, pleuritis and pneumonia may occur.  LABORATORY DIAGNOSIS 1. Stool examination: Diagnosis based on faecal examination, which reveals mainly trophozoites in acutely infected patients and cysts in chronic cases and carriers. It is generally easy to recognize B. coli in stool specimens because of its large size (60 x 45 𝜇m or more), an outer membrane covered with short cilia, and its large kidney- shaped macronucleus. When observed in wet mounts, the trophozoite has a rotatory, boring motility. In i0dine mounts, the trophozoite stains yellow-brown, and the macronucleus is easily visible. The cyst (40 - 60 𝜇m in diameter) can also be recognized by the large macronucleus. 2. Biopsy: Diagnosis can also be made by the examination of biopsy specimens taken with the help of a sigmoidoscope or by examination of scrapings of an ulcer. 3. Culture: Balantidium can be cultured in all the media that support the growth of Entamoeba histolytica. However, culture is rarely attempted for diagnosis as the parasites are more easily detected in faeces by microscopy and in tissues on histological examination.  TREATMENT Tetracycline 500 mg four times a day for 10 days or metronidazole 750 mg three times a day may be used for the treatment of B. coli infection. Prophylaxis Preventive measures include: Hygienic rearing of pigs and preventing the buman-pig contact which can lead to human infection. Prevention of contamination of food and water with pig and human faeces. Treatment of humans shedding cysts. This will prevent, human-to- hụman transmission